This invention relates generally to the field of spark plug gaskets, and more particularly to an improved captive type which remains in engaged condition upon the threaded shank of a spark plug body during installation and removal. The spark plug gasket art is presently at a highly developed state, and the invention lies in specific constructional details permitting improved reliability with respect to captivity.
It is known in the art to provide gaskets having staked out portions which deform upon installation of the plug within a cylinder head opening to captivate the gasket prior to removal, as illustrated, for example, in my prior U.S. Pat. No. 3,099,456 granted July 30, 1963. It is also known, as shown in my prior U.S. Pat. Nos. 3,156,477 granted Nov. 10, 1964; and 3,299,504 granted June 24, 1967, to provide a staking tool for deforming a locking flange forming part of a gasket to an undercut-engaging position to achieve captivation of the gasket prior to plug installation.
In order to be readily deformed under compression during installation, with adequate metal flow, gaskets of this type are normally formed from relatively thin gauge steel. The locking flange forming part of the gasket is normally of the same thicknesses as the blank from which the gasket is formed. When a plug has remained in installed condition over a relatively long period of time, rust, grime, and other substances tend to adhere the gasket in position bordering the spark plug opening recess. In such cases, when an attempt is made to remove the plug, the locking projections on the gasket instead of remaining attached to the plug body on occasion tend to "cross-thread" upon the threaded shank of the plug body, and unthread with rotation of the shank to remain in situ. This condition often remains undiscovered through failure to observe the shank of the plug removed, and when the replacement plug is engaged it is impossible to properly seal the same because of the presence of the additional unremoved gasket, as a result of which the electrodes of the spark plug are not properly positioned within the cylinder, and improper sealing may occur.